Modified atmosphere packaging for seafood

ABSTRACT

A method of packaging live seafood comprises the steps providing a sealable container placing the live seafood in the container and replacing the atmospheric gas in the container with a gas mixture comprising CO 2  and O 2  content of at least 50% and a CO 2  content of at least 20%.

CROSS REFERENCE TO RELATED APPLICATION

This application claims priority to Canadian Patent Application No. 2,489,738 filed Dec. 10, 2004.

BACKGROUND OF THE INVENTION

The present invention relates to the field of live seafood packaging. In particular, the present invention provides an improved live seafood packaging method and package that improves mortality rate of packaged live seafood, as compared with know live seafood packaging.

In the marketing of seafood, in particular shellfish, crustaceans and mollusks, it is very desirable to deliver a live product, to permit a restaurant or seafood market to offer the best possible seafood to the consuming public. Bringing live seafood to inland markets can be problematic and expensive. The most obvious and expensive, way to do so is to expedite transport of the live animals by air, preferably in an aqueous environment simulating their natural environment. This is effective, but expensive, because of the weight involved.

There have been several packaging methods proposed to keep live seafood alive during transit. In JP58129930, the product is packaged in a mixture of O₂ and CO₂ after it has been injected with alkaline solution of pH 7-12. This method, then, requires additional handling of each item and the use of an additive thereto, and is therefore, not economically feasible.

In U.S. Pat. No. 6,238,716, a packaging method using 50%-90% of a CO₂ and O₂ mix including 25%-50% O₂ is proposed. It has been found to be effective on some shellfish, but as will be discussed below, is ineffective in relatively long time frame shipping and storage.

SUMMARY OF THE INVENTION

The present invention provides a method of packaging, and resulting package that is particularly effective for long time frame shipping and storage of seafood. The method of the present invention results in very low mortality rates over twenty or more days of storage, making the present invention effective for large scale packaging of live seafood species for shipment to inland locations, utilizing low cost transit options.

In a broad aspect, the present invention relates to a method of packaging live seafood comprising the steps providing a sealable container, placing said live seafood in said container, and replacing the atmospheric gas in said container with a gas mixture comprising CO₂ and O₂, with an O₂ content of at least 50%, and a CO₂ content of at least 20%.

The sealable container will preferably include at least one layer made from flexible film. The container may be made from two sheets of flexible film sealed around their edges to provide an interior space between the two sheets.

Moreover, the container may comprise a plastic tray having an interior volume and an upper peripheral edge, with a sheet of flexible sealable film sealed to the upper peripheral edge of the tray.

In either event, the flexible film is preferably a multi-layer high barrier film.

The gas mixture used in the present invention may comprise at least 75% O₂, and preferably comprises about 80% O₂.

In a preferred form of the present invention, the balance of gas in the gas mixture, apart from O₂ is CO₂.

The packaging method of the present invention, in a practical embodiment, includes the further step of rinsing the live seafood with CIO₂ before placing same in the packaging.

The live seafood may be a bivalve mollusk selected from the group consisting of clams, mussels and oysters.

Typically, the live seafood is mussels.

The method of the present invention, whether using a sealed plastic tray, or a sealed bag type of package, is suitable for use on any existing packaging equipment in which the final atmosphere may be controlled.

DESCRIPTION OF THE DRAWINGS

In drawings that illustrate the present invention by way of example:

FIG. 1 is a flow diagram for modified atmosphere packaging of mussels;

FIG. 2 is a graph of mortality % vs. time, in days, for mussels stored at varying ratios of CO₂ and O₂;

FIG. 3 is a graph of mussel meat;pH vs. time, in days, for mussels stored at varying rates of CO₂ and O₂;

FIG. 4 is a graph of mussel drip pH vs. time, in days, for mussels stored at varying ratios of CO₂ and O₂;

FIG. 5 is a graph of mortality vs. the weight ratio of drip/mussel; and

FIG. 6 is a graph of pH of drip vs. weight ratio of drip/mussel.

DESCRIPTION OF A PREFERRED EMBODIMENT

In the method of the present invention, seafood, for instance blue mussels (Mytilus edulis) are packaged in modified atmosphere packaging (MAP) having a CO₂/O₂ ratio of less than 1:1, preferably less than 1:2, and preferably in the range of 1:4. The packaging method of the present invention is effectively illustrated by the following example.

Materials:

-   1. Eleven bags of 25 lbs. live mussels were harvested on Aug. 13,     2003 from PE3M area and delivered to the testing facility. The     temperature reading of the incoming samples was 7.3° C. by using a     Fluke Thermometer (5211 with type K thermocouples, Fluke     Corporation, USA). -   2. Two types of multilayer high barrier film (OF-900M for forming     the trays and OF-475M for sealing, both made of Nylon/EVOH/mpE)     sourced from the Packaging Group (Concord, ON) were used. -   3. One cylinder of food grade oxygen and one cylinder of carbon     dioxide. -   4.500 mL of 1.5 ppm chlorine dioxide solution.

Methods: Seven gas mixtures of different ratios of CO_(2/O) ₂ were used. The gas mixture levels are listed in Table 1. A Multivac gas mixer (Model KM-100-3M) was used to produce the desired proportions of CO₂ and O₂ in the package. TABLE 1 Gas Mixture levels for mortality rate study of MAP mussels. Gas Level, v/v % O₂ 20 30 40 50 60 70 80 CO₂ 80 70 60 50 40 30 20

FIG. 1 shows the flow diagram for the Modified Atmosphere Packaging (MAP) process. The Dixie Reiser package system (Reiser DV 2000E, Dixie Union Germany) was used for thermoforming of the trays and the sealing of the package using the multilayer high barrier films (OF-900M and OF475M) with the desired gas mixture. About 1.5 lb (681 g) of live mussels were used for each package. Twenty-two packages were prepared for each gas mixture level. A total of 154 packages for the 7 gas mixture levels were packed.

All MAP packed mussels were stored at 3° C. On every second day, two packages of each gas mixture were used for mortality evaluation by FTC staff and client. The pH values of mussel meat and drip in the packages were checked by using a Corning pH/ion meter (Model 155, Corning Inc., Corning, N.Y.). The head space gas composition of the package was also measured by using a Gas Analyser (MAPtest 4050, Hitech Instruments, Luton England).

Table 2 is the summary of data for mortality of the MAP mussels. TABLE 2 Day 0 2 4 6 8 10 12 14 16 18 20 CO₂/O₂ = 80/20 Head space gases O₂ % 22.9 29.6 29.4 32.4 28.4 27.8 27.4 26.3 23.8 22.0 21.3 CO₂ % 72.4 65.7 65.7 62.5 65.8 65.8 65.7 67.5 70.0 71.6 84.9 N₂ % 4.7 4.7 4.9 5.1 5.8 6.4 6.9 6.2 6.2 6.4 8.8 Drip/mussels (g/g) 3.18 12.63 10.23 12.13 13.72 12.17 23.50 17.12 22.36 18.09 23.00 Mortality, % 0.0 51.3 57.9 55.2 50.7 72.1 55.9 45.8 78.0 82.0 77.7 PH of mussel meat 6.3 6.2 6.7 6.4 6.6 6.5 6.8 6.8 6.5 6.6 6.5 PH of drip 6.2 6.1 6.2 6.3 6.3 6.1 6.5 6.6 6.4 6.4 6.4 CO₂/O₂ = 70/30 Head space gases O₂ % 32.7 40.2 38.7 39.0 41.3 38.9 37.4 35.0 33.1 29.8 28.1 CO₂ % 63.8 56.5 56.8 54.6 52.8 55.6 56.7 58.9 60.4 59.6 61.7 N₂ % 3.5 3.3 4.5 6.4 5.9 5.5 5.9 6.1 6.5 10/6 10.2 Drip/mussels (g/g) 5.54 10.68 8.44 9.43 11.39 11.00 18.74 19.03 17.53 20.19 19.90 Mortality, % 2.0 52.8 43.8 38.5 23.4 45.2 34.9 23.7 62.2 61.0 60.8 PH of mussel meat 6.3 6.4 6.4 6.5 6.5 6.4 7.2 6.6 6.6 6.5 6.8 PH of drip 6.1 6.4 6.3 6.4 6.4 6.2 6.7 6.6 6.5 6.6 6.5 CO₂/O₂ = 60/40 Head space gases O₂ % 36.7 42.5 53.0 58.1 54.4 54.0 47.9 49.2 45.2 46.6 41.5 CO₂ % 35.0 25.1 31.5 31.2 27.7 32.1 36.3 34.5 44.5 38.8 37.6 N₂ % 28.3 32.4 15.5 10.7 17.9 13.9 15.8 16.3 10.3 14.6 20.9 Drip/mussels (g/g) 6.83 12.45 6.16 4.40 4.82 3.02 18.05 16.09 16.95 12.56 12.40 Mortality, % 0.0 24.6 32.1 4.0 2.1 14.1 8.4 6.3 29.2 32.8 40.0 PH of mussel meat 6.5 6.5 6.6 6.4 6.6 6.6 7.0 6.8 6.7 6.6 6.4 PH of drip 6.5 6.4 6.6 6.7 6.7 6.9 6.7 6.8 6.5 6.5 6.5 CO₂/O₂ = 50/50 Head space gases 0₂ % 50.6 56.9 59.0 58.0 38.3 56.5 53.4 52.1 52.1 47.5 44.2 CO₂ % 45.4 39.3 35.9 36.1 23.7 37.2 41.2 40.6 41.2 45.7 45.7 N₂ % 4.0 3.8 5.1 5.9 3.8 6.3 5.4 7.3 6.7 6.8 10.1 Drip/mussels (g/g) 4.00 12.14 7.82 6.78 12.25 11.82 18.46 14.40 18.17 19.67 20.35 Mortality, % 0.0 44.0 37.5 10.9 12.3 32.7 12.4 7.9 26.9 44.8 35.7 PH of mussel meat 6.5 6.4 6.6 6.5 6.9 6.6 7.1 7.1 6.7 6.7 7.1 PH of drip 6.3 6.1 6.4 6.5 6.7 6.4 6.8 6.9 6.7 6.7 6.5 CO₂/0₂ = 40/60 Head space gases 0₂ % 60.5 66.7 68.9 65.6 64.3 63.1 62.3 59.8 57.6 57.9 51.9 CO₂ % 36.3 28.7 26.7 29.3 30.3 29.9 31.5 33.8 35.9 37.9 36.8 N₂ % 3.2 4.6 4.4 5.2 5.4 7.0 6.2 6.4 6.5 6.7 11.3 Drip/mussels (g/g) 2.96 14.28 6.7 6.61 10.76 9.01 16.00 13.80 16.20 14.81 18.54 Mortality, % 0.0 26.0 28.0 15.0 19.7 13.5 0.0 1.9 16.2 17.0 12.0 PH of mussel meat 6.4 6.4 6.7 6.5 6.6 6.7 6.9 7.0 7.0 6.9 7.0 PH of drip 6.4 6.3 6.6 7.0 6.6 6.5 7.0 7.0 6.9 6.9 6.8 CO₂/0₂ = 30/70 Head 0₂ % 68.8 74.4 74.6 74.4 72.7 70.6 69.4 68.2 62.9 62.9 59.9 space CO₂ % 57.5 21.2 20.5 20.5 21.4 22.9 24.9 25.6 30.9 30.8 29.5 gases N₂ % 3.7 4.4 4.9 5.1 5.9 6.5 5.7 6.2 6.2 6.3 10.6 Drip/mussels 2.35 12.03 6.75 12.41 9.82 9.51 16.72 18.56 16.88 19.15 19.32 (g/g) Mortality, % 1.9 7.7 17.3 6.0 18.7 11.3 2.0 0.0 5.7 13.9 0.0 PH of mussel 6.6 6.5 6.6 6.7 6.6 6.8 7.2 7.3 7.0 7.1 7.1 meat PH of drip 6.8 6.4 6.7 6.6 6.7 6.6 7.2 7.0 6.9 7.0 7.0 CO₂/O₂ = 20/80 Head O₂ % 78.7 81.2 81.8 79.9 78.5 74.8 74.0 70.1 66.6 66.2 61.1 space CO₂ % 18.6 13.5 13.4 15.5 16.5 18.9 19.1 23.0 25.9 27.3 26.3 gases N₂ % 2.7 5.3 4.8 4.6 5.0 6.3 6.9 6.9 7.5 6.5 12.6 Drip/mussels 2.41 9.66 9.41 12.59 13.30 9.97 19.02 15.59 13.94 16.82 14.85 (g/g) Mortality, % 1.9 3.9 7.5 0.0 22.0 9.5 0.0 0.0 4.0 5.9 0.0 PH of mussel 6.5 6.5 6.9 6.8 6.8 6.8 7.2 7.4 7.1 7.4 7.1 meat PH of drip 6.9 6.5 6.7 6.7 6.7 6.6 7.3 7.1 7.1 7.1 7.1

The lowest mortality rate was with the 20% CO₂ and 80% O₂ initial gas mixture. FIG. 2 shows the mortality rate of MAP mussels with different gas mixture levels. Generally, there is a higher mortality rate during the storage time with higher CO₂ concentration in the packages. The fluctuation in mortality rate during the course of evaluation was partially due to the slow response of some mussels to tapping, which was used to determine the status of the mussels.

Generally, the oxygen levels were slightly decreased during the course of storage while the carbon dioxide content in all MAP packages decreased in the first few days and then increased slightly. The nitrogen contents in the packages increased with the storage time in all the gas mixture levels. The decreased of O₂ is apparently due to the activity of mussels as a result of respiration. The increase in N₂ is possibly a result of permeation of the packages from atmospheric gas. This would suggest that the change in O₂ might also be due to permeation through the package in addition to consumption by the mussels. This indicates tight film may be desirable.

The pH values of mussel meat and drip with different gas mixture levels are shown in FIG. 3. It is clear that the higher carbon dioxide content in the package had the lower pH in the meat and drip. The pH on the meat and in the drip had a trend toward increasing with the storage time with most of the gas mixtures. It may extend the shelf life of mussels by effectively adding an acid solution in the MAP package.

FIG. 4 shows the plots for mortality and pH of the drip vs. the weight ratio of drip to mussels with different gas mixture levels. The patterns seem to indicate that the relations were random, as the ratio of pH of drip to pH of mussel, as shown in FIG. 5.

Overall, the 20% O₂-80% CO₂ and 30% O₂-70% CO₂ initial gas mixtures gave the very low mortality rate (close to 0%) of the mussels during the 20-day storage using the described packages and at 3° C. storage condition.

In view of these results, it will be appreciated that enriching the O₂ content of the packaging atmosphere has demonstrable results in terms of enhances viability of the seafood product being shipped. 

1. A method of packaging live seafood comprising the steps of: providing a sealable container, placing said live seafood in said container, and replacing the atmospheric gas in said container with a gas mixture comprising CO₂ and O₂, with an O₂ content of at least 50%, and a CO₂ content of at least 20%.
 2. A method as claimed in claim 1 wherein said sealable container includes at least one layer made from flexible film.
 3. A method as claimed in claim 2 wherein said container is made from two sheets of flexible film sealable around their edges to provide an interior space between said two sheets.
 4. A method as claimed in claim 2 wherein said container comprises a plastic tray having an interior volume and an upper peripheral edge, and a sheet of flexible sealable film sealed to the upper edge of said tray.
 5. A method as claimed in claim 3 wherein said flexible film is a multi-layer high barrier film.
 6. A method as claimed in claim 1 wherein said gas mixture comprises at least 75% O₂.
 7. A method as claimed in claim 1 wherein said gas mixture comprises about 80% O₂.
 8. A method as claimed in claim 1 wherein the balance of gas in said gas mixture, apart from O₂, is CO₂.
 9. A method as claimed in claim 1 including the further steps of rinsing said live seafood with CIO₂ before placing same in said packaging.
 10. A method as claimed in claim 1 wherein said live seafood is a bivalve mollusk selected from the group consisting of clams, mussels and oysters.
 11. A method as claimed in claim 1 wherein said live seafood is mussels.
 12. A package produced by the method of claim
 1. 13. A packaged seafood product comprising a package produced by the method of claim 1 enclosing a live seafood product selected from the group consisting of clams, oysters and mussels.
 14. The package as claimed in claim 12 including a rinse aliquot of CIO₂ for application on the seafood organism before placing said organism in said package.
 15. A packaged seafood product comprising: a sealable container for holding a live seafood organism, an internal container atmosphere of a gas mixture comprising CO₂ and O₂, with an O₂ content of at least 50%, and a CO₂ content of at least 20%, and a live seafood product.
 16. The packaged seafood product as claimed in claim 15 wherein said sealable container includes at least one layer made from flexible film.
 17. The packaged seafood product as claimed in claim 15 wherein said container is made from two sheets of flexible film sealable around their edges to provide an interior space between said two sheets.
 18. The packaged seafood product as claimed in claim 15 wherein said container comprises a plastic tray having an interior volume and an upper peripheral edge, and a sheet of flexible sealable film sealed to the upper edge of said tray.
 19. The packaged seafood product as claimed in claim 15 wherein said gas mixture comprises at least 75% O₂.
 20. The packaged seafood product as claimed in claim 15 including the further steps of rinsing said live seafood with CIO₂ before placing same in said packaging. 